1. Field of the Invention
This invention relates to roll designs, specifically to rolls for high temperature roller hearth furnaces.
2. Description of the Prior Art
In low temperature applications, less than 1100.degree. C., non-water cooled alloy rolls are normally successfully utilized. At temperatures between 1100.degree.-1200.degree. C., rolls have been utilized for thin slabs where a water cooled shaft is equipped with a plurality of spaced tires welded to the shaft, wherein the roll is insulated with refractory clams.
The problems encountered with these prior art high temperature rolls are refractory failure, which generates bowing of the shaft and failure of the tires. Following tire failure, it is difficult to repair the roll. Removing and rewelding a tire are difficult without distorting the main shaft. In addition, these prior art rolls were not designed to handle heavy loads.
Additionally, at temperatures between 1100.degree.-1200.degree. C., non-water cooled rollers have been used in some occasions; however, drawbacks exist because of the limited strength of material at that temperature (roll failure could occur if the rolls are stopped from rotating). Also, at temperatures of about 1200.degree. C., scale pickup starts becoming a problem.
For temperatures above 1200.degree. C., roll designs encounter several additional problems. At these higher temperatures, the tires encounter greater steel scale pickup problems and the insulation life is further reduced. Additionally, the tires may be subject to cracks due to thermal stresses and fatigue.
The present invention has the purpose of overcoming the drawbacks of the prior art.